1. Field of the invention
The present invention concerns a system for guiding vehicles, in particular public transport vehicles, on a virtual track by means of a magnetic field generated by a field emitting device disposed on the axis of the track to be followed and comprising two magnetic sensors receiving the field disposed on the vehicle.
2. Description of the prior art
There is already known a technique for laterally guiding vehicles, in particular trolleys for conveying objects in factories, by means of a magnetic field emitted by an electrically conductive wire disposed on the axis of the track to be followed by the vehicle. The vehicle is fitted with at least one pair of coils for sensing the field generated by the wire. A technique of this kind is described in the document FR-A-2278525, for example.
There is also described in the publication Recherche Transports Securite, Mar. 1984, p. 45-47 a bus guidance electronic device (the so-called "Spurbus project") using the circular magnetic field generated by a cable carrying a low-frequency low-amperage current. There are disposed in the vehicle at the same height two perpendicular coils with their axis respectively horizontal and vertical connected to units for sensing phase differences between the voltages induced by the field.
Systems of this kind provide satisfactory lateral guidance of vehicles but are of no utility if it also required to monitor their speed and their position.
For this type of guidance use must be made of a radio transmission system or a system using microwave waveguides parallel to the track to be followed by the vehicle, the microwave guidance system being the subject matter of French patent application FR-A-2612715 dated Mar. 18, 1987.
This patent provided for disposing the microwave waveguide either laterally of the track to be followed or buried on its axis.
However, it was not feasible to use a microwave waveguide buried on the axis of the track to be followed to procure additionally lateral guiding of the vehicle as it could be foreseen that the accuracy of any such guidance would be very poor, the uncertainty as to the correct lateral position possibly being in the same order of magnitude at least as the width of the waveguide.
An object of the present invention is to provide a system for guiding vehicles on a virtual track which procures in addition to position and/or speed guidance accurate lateral guidance as would be necessary for public transport vehicles in particular.